1. Field of the Invention
One embodiment of the present invention relates to a method for forming a separation starting point and a separation method.
Note that one embodiment of the present invention is not limited to the above technical field. Examples of the technical field of one embodiment of the present invention include a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, an electronic device, a lighting device, an input device (e.g., a touch sensor), an input/output device (e.g., a touch panel), a method for driving any of them, and a method for manufacturing any of them.
2. Description of the Related Art
In recent years, a flexible device in which a functional element such as a semiconductor element, a display element, or a light-emitting element is provided over a substrate having flexibility (hereinafter also referred to as a flexible substrate) has been developed. Typical examples of the flexible device include, as well as a lighting device and an image display device, a variety of semiconductor circuits including a semiconductor element such as a transistor.
As a method for manufacturing a device including a flexible substrate, a technique has been developed in which a functional element such as a thin film transistor or an electroluminescence (EL) element is formed over a formation substrate (e.g., a glass substrate or a quartz substrate), and then the functional element is transferred to a flexible substrate. This technique needs a step of separating a layer to be separated including the functional element from the formation substrate (referred to as a separation step).
For example, Patent Document 1 discloses the following separation technique using laser ablation: a separation layer formed of amorphous silicon or the like is provided over a substrate, a layer to be separated that includes a thin film element is provided over the separation layer, and the layer to be separated is bonded to a transfer body with the use of an adhesive layer. The separation layer is ablated by laser irradiation, so that separation is generated in the separation layer.
In addition, Patent Document 2 discloses a technique in which separation is conducted by physical force with human hands or the like. Patent Document 2 discloses the following separation technique: a metal layer is formed between a substrate and an oxide layer, and separation is generated at an interface between the oxide layer and the metal layer by utilizing a weak bonding between the oxide layer and the metal layer, whereby a layer to be separated and the substrate are separated from each other.